Adjective
1. beginning
2. opening
5. inceptive
6. embryonic
8. first
9. early
10. primary
11. preliminary
12. elementary
13. foundational
14. preparatory
15. introductory
16. inaugural
Verb
17. put one's initials on
18. initialize
19. sign
20. ink
21. countersign
22. autograph
23. endorse
24. inscribe
25. witness
26. verify